1. Field of the Invention
The present invention relates to an oil pump of a hermetic compressor, and more particularly, to an oil pumping device of a hermetic compressor using a trochoid pump so as to pump oil by using a variation in volume.
2. Description of the Background Art
In, general, a hermetic compressor includes a compression part and a motor part inside a hermetic casing. When the compression part operates by a driving force of a motor part, the compressor part sucks, compresses, and discharges refrigerant. Recently, in order to minimize environmental pollution, such as global warming, the use of CFC-based refrigerant has been gradually regulated in the hermetic compressor field. Therefore, in order to minimize the environment pollution and improve efficiency of the compressor, alternative refrigerants have been used. Also, research on different oils suitable for the alternative refrigerants has been performed.
The type of oil influences the performance of sliding parts. When oil is easily separated from the refrigerant, the refrigerant, having a higher density, flows downward due to gravity. If the oil pump of such a compressor pulls oil from the bottom of the compressor casing, this can result in the sliding parts being supplied with more refrigerant than oil. As a result, abrasion of the sliding parts may be increased due to lack of oil.
FIG. 1 is a longitudinal sectional diagram illustrating one embodiment of a scroll compressor using a centrifugal oil pump according to the related art. As shown therein, the related art scroll compressor includes a casing 1 filled with a predetermined amount of oil, a main frame 2 and a sub-frame 3 that are fixed to upper and lower sides, respectively, inside the casing 1/A driving shaft 4 is coupled with a rotor of a driving motor (M) mounted between the main frame 2 and the sub-frame 3 so as to transmit a rotary force. An orbiting scroll 5 is eccentrically coupled with the driving shaft 4 of the driving motor (M) and performs an orbiting motion at an upper surface of the main frame 2. A fixed scroll 6 is fixed to the main frame 2 so as to be engaged with the orbiting scroll 5 so as to form a plurality of compression chambers (P) with the orbiting scroll 5. An Oldham's ring 7 is installed between the orbiting scroll 5 and the main frame 2 so as to prevent rotation of the orbiting scroll 5 and allow the orbiting scroll to perform an orbiting motion. A check valve 8 is coupled to a rear surface of an end plate portion of the fixed scroll 6 so as to prevent backflow of compression gas. A centrifugal oil pump 9 is installed under the driving shaft 4 and acts to pump oil within the casing 1 by a centrifugal force generated by rotation of the driving shaft 4.
An internal space of the casing 1 is divided into a suction area (S1) which is a low pressure part, and a discharge area (S2) which is a high pressure part by a high and low pressure separation plate 1a that is fixed to an upper surface of the fixed scroll 6. A gas suction pipe (SP) is connected to the suction area (S1), while a gas discharge pipe (DP) is connected to the discharge area (S2).
The driving shaft 4 includes a shaft portion 4a coupled with the rotor (Mr), a driving pin portion 4b eccentrically protruding from an upper end of the shaft portion 4a and coupled to the orbiting scroll 5, and an oil path 4c penetrating the driving shaft 4 from a lower end of the shaft portion 4a to an upper end of the driving pin portion 4b so as to guide oil which is pumped by the oil pump 9. 5a and 6a denote a wrap of the orbiting scroll and a wrap of the fixed scroll, respectively. Also, Ms denotes a stator of the motor M.
The oil pump 9 is fixed to a lower end of the oil path 4c. The oil pump 9 is a centrifugal oil pump, which includes a propeller. The oil pump 9 rotates together with the driving shaft 4, when the driving shaft 4 rotates, so as to pump the oil in the casing 1 by the centrifugal force.
When power is applied to the driving motor (M) and the driving shaft 4 rotates, the orbiting scroll 5 at the upper surface of the main frame 2 orbits, to thereby form a pair of compression chambers (P), which continuously move toward the center, between the wrap 5a of the orbiting scroll 5 and the wrap 6a of the fixed scroll 6. The compression chambers (P) move toward the center by the continuous orbiting movement of the orbiting scroll 5 so as to reduce a volume thereof. Here, after refrigerant gas is sucked and compressed, the compressed gas is discharged into the casing 1.
At this time, oil is pumped by the centrifugal force of the centrifugal oil pump 9 when the driving shaft 4 rotates at a high speed, and the pumped oil is forced up though the oil path 4c. Some oil lubricates between the main frame 2 and the driving shaft 4, and other oil is scattered from the upper end of the driving shaft 4 so as to lubricate between the main frame 2 and the orbiting scroll 5.
Because the oil pump 9 is a centrifugal oil pump that pumps oil using centrifugal force, it is possible for the oil pump 9 to smoothly pump the oil during high-speed operations. However, during low-speed operations, the centrifugal force decreases, and it may be impossible for the oil pump 9 to smoothly pump the oil. Therefore, during low speed operations, abrasion between components is caused by lack of oil in the sliding parts, and reliability and performance of the compressor may be reduced.
In addition, when the refrigerant and oil are completely mixed with each other, the oil can smoothly be pumped regardless of how deeply the oil pump 9 sinks under the oil. However, a ‘double-layer separation phenomenon’ may occur. That is, the refrigerant and the oil separate form each other due to density differences. The refrigerant, having relatively high density, is deposited at the bottom of the two layers. Therefore, the oil pump 9 mostly pumps the refrigerant and fails to pump the oil. This increases abrasion caused by lack of oil in each of the sliding parts. Therefore, reliability and performance of the compressor are seriously reduced.